Someone had asked what types of apps you can develop on Android.
You can develop Hybrid Mobile Web apps that contain both native and web code, I am developing a Loopt clone called Xspot:
Xspot Video
Another one I am developing is a replacement for Android's HomeScreen with a widget system called Zyle:
Zyle Video
These are just a few of the different applications you can develop for Android.
You will find the knols I am writing about Android Programming at:
Fred Grott's Knols